This disclosure generally relates to a sensor holder to be applied on an appendage of a subject. The sensor holder comprises a substrate with at least a first location for a first sensor component. The substrate surrounds a hollow for receiving the appendage along a longitudinal axis of the hollow.
The concentration of substances, such as oxygen, in tissue is typically measured non-invasively by measuring the absorption of light at different wavelengths in the tissue. By calculating the ratio of absorption for different wavelengths, the concentration of a substance can be calculated, e.g. absorption ratio of red and infrared light is used to determine the concentration of oxygenated blood. Typically, what is measured is the color of the tissue. In the case of oxygenation, the tissue becomes darker red at lower saturations and brighter red at higher saturations. The different colors of the tissue absorb light of different wavelengths (color) differently, and by measuring these absorptions, the relative concentration can be calculated. By measuring more or other wavelength absorptions, more substance concentrations can be calculated in the same manner. The light is typically emitted using light emitting diodes (LED's) of different wavelengths and detected using a photodetector (e.g. photodiode).
In a typical implementation, the LED's of different wavelength are lit up in sequence, making it possible to measure the absorption of each wavelength using a single photodetector which is sensitive over a wide wavelength range. Short pulses are typically used to maximize optical output power while limiting the total power to prevent heating of the optical components. Typical wavelengths used for SpO2 measurement are 650 . . . 670 nm for red and 880 . . . 950 nm for infrared.
Semiconductive light emitting diodes (LED's) are typically used as light sources for SpO2 sensors. The LED's used in SpO2 sensors today are manufactured on a wafer and diced into small chips that are mounted on a substrate. The typical manufacturing process involves bonding the chip to a substrate using a conductive adhesive, curing the adhesive in an oven, bonding a gold wire from the top of the chip to a contact pad on the substrate and finally encapsulating the whole assembly in a clear encapsulant. To be able to utilize this assembly in an SpO2 sensor, it must further be connected to electrical conductors connecting the LED electrodes to an SpO2 monitor. This is typically done using soldering or wire welding.
There are generally two types of sensors used for this purpose, reusable and disposable. The reusable sensors are typically clip-on sensors that use a spring force to keep the sensor on the patient or alternatively there is an additional accessory for applying the sensor to the patient. Disposable sensors are typically adhesive and are adhered to or wrapped around the area of the patient where the measurement is done. Common for both sensor types is that they apply pressure on the sensor site and cover the patient's skin. Adhesives are also known to cause skin reactions especially during prolonged use. To mitigate potential side-effects of this, such as pressure necrosis or skin symptoms, manufacturers typically recommend switching the sensor site every few hours. With reusable sensors, this is easily accomplished, but with adhesive disposable sensors, the performance of the adhesive degrades with each removal and there is typically adhesive residue at the former sensor site.